This invention relates to the production of titanium tetrachloride, namely TiCl4. More particularly, the invention relates to a process for the production of TiCl4, which is useful in the production of titanium metal or titanium dioxide, by the chlorination of titanium values in a titanium-containing starting material.
According to the invention there is provided a process for the production of titanium tetrachloride (TiCl4) by the chlorination of titanium values in a titanium-containing starting material, the process including the steps of:
exposing the starting material to a chlorinating agent; and
contacting the starting material with an inert liquid, while the starting material is exposed to the chlorinating agent, the inert liquid being at a temperature of 200-350xc2x0 C. and being at a pressure of 5-100 atmospheres (1 atmosphere=101.325 kN/m2), to cause the starting material to react with the chlorinating agent to form TiCl4.
Preferably the temperature is 225-300xc2x0 C., eg 230-290xc2x0 C. and the pressure is preferably 6-50 atmospheres, eg 10-50 atmospheres. Contacting the starting material with the inert liquid may be by immersing the starting material in the inert liquid.
The starting material may be in the particulate solid form, preferably finely divided solid form, with a particle size of less than 3000xcexcm, preferably less than 100xcexcm, the starting material having an average particle size of 1-3000xcexcm, preferably 50-100xcexcm. The process may accordingly include, as a preliminary step, size reduction of the solid starting material, for example by milling, to achieve the above maximum and average particle sizes. Immersing the particulate starting material may thus be by suspending particles thereof in the inert liquid, conveniently to form a slurry, for example a slurry in which the suspended particles form 2-50% by volume, preferably 10-30%. In other words, contacting the starting material with the inert liquid may be by immersing it as a suspension in the inert liquid to form a slurry, suspended particles of the starting material in the slurry forming 2-50% by volume of the slurry.
Suitable starting materials may include carbides of titanium, nitrides of titanium, carbonitrides of titanium, titanium monoxide (TiO), oxycarbonitrides of titanium (particularly those wherein the predominant titanium-containing crystals are in the cubic phase, such as Ti(Ox, Cy, Nz) in which x+y+z=1, and mixtures of the aforegoing.
By an inert liquid is meant a liquid which reacts unacceptably neither with the starting material nor with any chlorinating agent or reductant in the reaction mixture at the reaction temperature and reaction pressure. The inert liquid may thus be a fully chlorinated liquid substrate, which is not prone to being further chlorinated, examples being SiCl4, VCl4, VOCl3, and in particular, TiCl4 itself, so that the inert liquid may be selected from the group consisting of SiCl4, VCl4, VOCl3, TiCl4 and mixtures thereof.
The chlorinating agent may be a suitable chlorine-containing compound, such as a chlorine-containing liquid or particularly a chlorine-containing gas. Examples of suitable chlorinating agents are HCl, CCl4, SCl2, and, in particular, molecular chlorine gas, namely Cl2. The chlorinating agent may thus be selected from the group consisting of HCl, CCl4, SCl2, Cl2 and mixtures thereof. The chlorinating agent may be dispersed in the inert liquid, eg TiN, by dissolving it and/or dispersing globules or bubbles thereof in the inert liquid, conveniently under stirred and preferably turbulent conditions, to promote thorough mixing of the reaction mixture and contact between its reactive constituents, particularly between the starting material and the chlorinating agent. In other words, the chlorinating agent may be dispersed as a disperse phase in the inert liquid which forms a continuous phase, the inert liquid being agitated to promote dispersion of the chlorinating agent therein; and the agitation may be such as to produce turbulent conditions in the inert liquid to promote maintenance of homogeneous reaction mixture and rapid reaction between the starting material and the chlorinating agent.
The process may be carried out batchwise, or it may be carried out on a continuous basis.
When the process is carried out batchwise, it may be carried out in a reactor such as a temperature-controlled pressure vessel which is stirred or otherwise agitated, the pressure vessel containing a charge of inert liquid such as TiCl4 and a charge of milled starting material having a maximum particle size of 100 xcexcm and an average particle size of 50-100 xcexcm, in which charge the starting material forms 10-30% by volume. The slurry may be heated to a temperature of at least 200xc2x0 C., molecular chlorine liquid or gas then being admitted to the pressure vessel until an operating pressure of 10-50 atmospheres is reached. The chlorine will act strongly exothermically with titanium values in the starting material, to produce TiCl4. TiCl4 in the vessel is permitted to boil at an operating temperature corresponding to the operating pressure, being vented as a constituent of a vapour from the pressure vessel to prevent the temperature and pressure in the vessel from exceeding the operating temperature and operating pressure respectively. Thus, in a particular embodiment, the process may be carried out batchwise in a pressure vessel in which the temperature and pressure are controlled and in which the inert liquid is agitated, the inert liquid being TiCl4, the starting material being a milled starting material having a maximum particle size of 100 xcexcm and an average particle size of 50-100 xcexcm and the starting material and inert liquid being present in a volume ratio of 10:90-30:70, the temperature being 225-300xc2x0 C. and the pressure being 6-50 atmospheres, and the chlorinating agent being molecular chlorine (Cl2), TiCl4 in the vessel being permitted to boil and being vented from the vessel, as it is produced, as a constituent of a vapour vented from the vessel, the venting being at a rate which keeps the temperature at a value of 225-300xc2x0 C. and keeps the pressure at 6-50 atmospheres.
The TiCl4 in the vented vapour can be regarded as product and can be condensed and separated from other constituents of the vented vapour, such as chlorine gas and other gases or vapours, the chlorine optionally being recovered for subsequent use in chlorinating another batch of starting material. Solid residues will remain in the pressure vessel, typically suspended in the inert liquid. The aforesaid batch reaction cycle can then be repeated, by loading a fresh charge of starting material into the vessel and chlorinating it as set forth above. Accumulated solid residues can be cleared periodically from the vessel; and the charge of inert liquid can be discarded and replaced, if and when it becomes unacceptably contaminated by dissolved or suspended impurities.
When the process is carried out continuously, a starting material such as titanium nitride, milled to a maximum particle size of 100 xcexcm and an average particle size of 50-100 xcexcm and mixed with an inert liquid such as TiCl4 to form a slurry in which the solid material forms 10-30% by volume. The slurry may then be heated to a temperature of at least 200xc2x0 C. as for batch operation and transferred, eg by pumping, to a suitable reactor operating at at least 200xc2x0 C. such as a temperature-controlled pressure vessel which is agitated, for example an upflow slurry bubble-column reactor which may be fitted with baffles to resist back mixing and to the bottom of which liquid or gaseous molecular chlorine is introduced as chlorinating agent, eg via a sparger. As is the case with batchwise operation, the introduced chlorine reacts with titanium values, in strongly exothermic fashion, to produce TiCl4. Thus, in another particular embodiment, the process may be carried out continuously, milled starting material of a maximum particle size of 100 xcexcm and average particle size of 50-100 xcexcm being mixed with TiCl4 as the inert liquid to form a slurry, the starting material and inert liquid being present in the slurry in a volume ratio of 10:90-30:70, the slurry being transferred at a temperature of at least 200xc2x0 C. to a temperature-controlled pressure vessel into which molecular chlorine is introduced as the chlorinating agent, TiCl4 being vented from the vessel, as it is produced, as a constituent of a vapour vented from the vessel, the venting being at a rate which keeps the temperature in the vessel at a value of 225-300xc2x0 C. and the pressure at 6-50 atmospheres.
TiCl4 and/or the inert liquid may be vented from the top of the column as part of a vapour, at a rate which controls the operating temperature in the column to a value of 225-300xc2x0 C., the TiCl4 and/or inert liquid being allowed to boil at an operating pressure of 6-50 atmospheres, corresponding to the operating temperature, bearing in mind that slurry feed is being introduced to the bottom of the reactor and spent slurry is being withdrawn from the top of the reactor. Gas vented from the reactor may have the TiCl4 therein condensed as product, some of which may be recycled to the reactor, directly into the slurry feed, directly into the reactor or indirectly via the mixing step where the slurry feed is formed. Similarly, the inert liquid (if a substance other than TiCl4 is used therefor)may be condensed and recycled to the reactor. Non-condensible gases from this condensation may, after extraction of any residual TiCl4 or chlorine gas therefrom, be discarded, the extracted TiCl4 and chlorine optionally being recycled to the reactor.
The spent slurry withdrawn from the top of the reactor may have the TiCl4 contained therein recovered, eg by filtration, the filtrate being TiCl4 which may be recycled to the initial slurry-forming mixing step, or to the slurry formed in the initial mixing step. Filter cake from the filtration step may then be dried, dried filter cake being subjected to waste treatment, eg to recover or neutralize salts such as FeCl2 or FeCl3 therein, before being discarded, and TiCl4 from the drying may be recovered and recycled together with the recycled filtrate.
A feature of the process, whether carried out continuously or batchwise, is that, at the relatively low operating temperatures of 200-350xc2x0 C., impurities such as silicates and aluminates are not chlorinated to any significant extent. Furthermore, in each case, a proportion of the introduced chlorine will dissolve in the TiCl4 in the reactor, the remainder existing as bubbles. Any metallic iron will tend to be chlorinated to either ferrous chloride or ferric chloride, ie FeCl2 or FeCl3, which have relatively low vapour pressures at the reaction temperatures of 200-350xc2x0 C., particularly if the reaction temperature is below 290xc2x0 C. Relatively little FeCl2 and FeCl3 will thus issue from the reaction as vapour with the product TiCl4 vapour, and the bulk thereof will remain dissolved in the TiCl4 of the slurry where it forms a saturated solution, or will form a solid constituent attached to solids in the slurry, issuing from the reactor as part of the solids residue, on which it can form a passivating layer.
The invention extends to titanium tetrachloride whenever produced according to the method described above.
The invention will now be described, by way of a non-limiting illustrative example, with reference to the accompanying diagrammatic drawings, in which:
FIG. 1 shows a schematic flow diagram of a batchwise process according to the present invention; and
FIG. 2 shows a schematic flow diagram of a proposed continuous process according to the present invention.